Electronic device, dielectric ceramic composition, and method for producing same

ABSTRACT

A dielectric ceramic composition comprising as main components barium titanate and a component M (wherein M is at least one type of component selected from manganese oxide, iron oxide, cobalt oxide, and nickel oxide) and having a ferroelectric phase region, wherein the concentration of the component M in the ferroelectric phase region changes from the outside toward the center. The concentration of the component M in the ferroelectric phase region is higher at the outside compared with near the center of the ferroelectric phase region. It is possible to realize a multi-layer capacitor which can satisfy both of the X7R characteristic (EIA standard) and B characteristic (EIAJ standard) of the temperature characteristic of the electrostatic capacity, has little voltage dependency of the electrostatic capacity and the insulation resistance, is superior in insulation breakdown resistance, and can use Ni or a Ni alloy as the internal electrode layer.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a multi-layer capacitor or otherelectronic device, a dielectric ceramic composition suitable for use asthe dielectric layer of the electronic device, and a method forproducing the same.

[0003] 2. Description of the Related Art

[0004] A multi-layer ceramic capacitor is being broadly used as acompact, large capacity, high reliability electronic device. The numberused in each piece of electrical equipment and electronic equipment hasalso become larger. In recent years, along with the increasingminiaturization and improved performance of equipment, there have beenincreasingly stronger demands for further reductions in size, increasesin capacity, reductions in price, and improvements in reliability inmulti-layer ceramic capacitors.

[0005] One of the key technologies for reducing price is the use of therelatively inexpensive Ni or Ni alloys instead of use of the high pricedPd and Pd alloys for the internal electrodes. Further, the keytechnologies for the reduction of size and the increase in capacity arethe reduction in thickness of the dielectric layer and the use ofmultiple layers.

[0006] If the thickness of the dielectric layer is reduced, the electricfield intensity acting on the dielectric layer when a DC voltage isapplied becomes larger. Along with this, the phenomenon of the reductionin the electrostatic capacity and the insulation resistance becomesremarkable—in particular in high dielectric constant dielectric ceramiccompositions. From previous reports on the DC voltage dependency of theelectrostatic capacity, that is, the DC bias, it is widely known to addto a main component of barium titanate, subcomponents such as Bi₂O₃,TiO₂, SnO₂, ZrO₂, and other compounds and rare earth elements. When adielectric ceramic composition containing these compounds assubcomponents is used as the dielectric layers in a multilayercapacitor, however, the Pd of the internal electrode layer and thesubcomponent compounds (for example, Bi₂O₃) react and thecharacteristics of the capacitor become insufficient. Therefore, it isnecessary to use Pt or Au, which are both more expensive than Pd, forthe internal electrode layers.

[0007] Further, as a dielectric ceramic composition not containing acompound such as Bi₂O₃, there are known dielectric ceramic compositionscomprising a main component of barium titanate and subcomponents ofNb₂O₅, Co₂O₃, Nd₂O₅, MnO₂, and SiO₂ (Japanese Unexamined PatentPublication (Kokai) No. 6-203630). A multilayer capacitor using thisdielectric ceramic composition as dielectric layers and using 30% Ag-70%Pd alloy as the internal electrodes has a temperature change of theelectrostatic capacity TCC which satisfies the X7R characteristic andhas a rate of change of the electrostatic capacity ΔC/C of within −30percent when applying a DC bias field of 2 kV/mm. It is difficult toapply this dielectric ceramic composition, however, to a multi-layercapacitor using Ni as internal electrode layers.

[0008] Note that, as shown in Japanese Unexamined Patent Publication(Kokai) No. 10-330160, to improve the insulation breakdown voltage,there is known a barium titanate-based dielectric ceramic compositionwherein Mn or another additive is substantially uniformly distributed inthe entire region from the grain boundary to center of the crystal grainhaving a core-shell structure. In such a dielectric ceramic composition,however, the dielectric constant is insufficient and the temperaturechange of the electrostatic capacity TCC does not always satisfy the X7Rcharacteristic of the EIA standard.

SUMMARY OF THE INVENTION

[0009] An object of the present invention is to provide an electronicdevice such as a multi-layer capacitor which can satisfy both of the X7Rcharacteristic (EIA standard) and B characteristic (EIAJ standard) ofthe temperature characteristic of the electrostatic capacity, has littlevoltage dependency of the electrostatic capacity and the insulationresistance, is superior in insulation breakdown resistance, and can useNi or a Ni alloy as the internal electrode layer, a dielectric ceramiccomposition suitable for use as the dielectric layer of such anelectronic device, and a method of producing the same.

[0010] The present inventores engaged in intensive studies to achievethe object and as a result discovered that a dielectric ceramiccomposition comprised of barium titanate and a component M as maincomponents and having a ferroelectric phase region in which theconcentration of the component M in the ferroelectric phase regionchanges from the outside toward the center has superior properties andthereby completed the present invention.

[0011] That is, according to the present invention, there is provided adielectric ceramic composition comprising as main components bariumtitanate and a component M (wherein M is at least one type of componentselected from manganese oxide, iron oxide, cobalt oxide, and nickeloxide) and having a ferroelectric phase region, wherein theconcentration of the component M in the ferroelectric phase regionchanges from the outside toward the center thereof.

[0012] The concentration of the component M in the ferroelectric phaseregion is preferably higher at the outside compared with near the centerof the region.

[0013] The ferroelectric phase region is preferably comprised of anoutside ferroelectric phase region and an inside ferroelectric phaseregion and has a higher concentration of the component M in the outsideferroelectric phase region than the inside ferroelectric phase region.In this case, more preferably, the inside ferroelectric phase regiondoes not contain almost any of the component M.

[0014] In the dielectric ceramic composition of the present invention,generally there is a diffusion phase region outside of the ferroelectricphase region.

[0015] According to the present invention, there is provided a method ofproducing a dielectric ceramic composition comprising the steps ofcalcining barium titanate (A) and an ingredient of a component M (whereM is at least one type of component selected from manganese oxide, ironoxide, cobalt oxide, and nickel oxide) and firing a mixture of thecompound obtained in the calcination step and other barium titanate (B).

[0016] The temperature at the calcination is preferably 1000 to 1300° C.

[0017] The firing may be performed under a reducing atmosphere.

[0018] The molar ratio (M/A) of the component M to the pre-calcinationbarium titanate (A) is preferably 0.0010 to 0.0120, more preferably0.0020 to 0.0080. Further, the molar ratio (B/A) of the later addingbarium titanate (B) with respect to the pre-calcination barium titanate(A) is preferably 0.05 to 5.00, more preferably 0.10 to 1.00.

[0019] According to the present invention, there is provided anelectronic device having a dielectric layer, wherein the dielectriclayer is comprised of the above dielectric ceramic composition.

[0020] In the present invention, the “ferroelectric phase region” meansthe inside of a portion where a boundary is observed inside of a crystalgrain when observing the microstructure of a dielectric ceramiccomposition by a transmission electron microscope (TEM). Theferroelectric property of barium titanate (BaTiO₃) is derived from thebipolar moment arising due to the displacement of the Ti ions. Whenatoms other than Ti atoms solidly dissolve into the barium titanate, thedielectric constant falls, the electrostatic capacity and the insulationresistance become blunted with respect to the voltage applied, and theferroelectric property falls.

[0021] Therefore, the inside ferroelectric phase where the concentrationof the component M is small contributes to an improvement of thedielectric constant, while the outside ferroelectric phase where theconcentration of the component M is high has a small ferroelectricproperty. The ferroelectric region in the dielectric ceramic compositionof the present invention is comprised of at least these two or moreferroelectric phases. As a result, it is possible to provide adielectric ceramic composition having a high dielectric constant, asmall temperature dependency of the electrostatic capacity, and smallvoltage dependencies of the electrostatic capacity and insulationresistance.

[0022] Note that when the concentration of the component M is relativelylow and the component is uniformly distributed in the ferroelectricphase region, the dielectric ceramic composition has a larger dielectricconstant, but there is the problem that the dielectric ceramiccomposition has a larger voltage dependency of the dielectric constant.Further, when the concentration of the component M is relatively highand the component is uniformly distributed in the ferroelectric phaseregion, the dielectric ceramic composition has a smaller voltagedependency, but also a lower dielectric constant.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] These and other objects and features of the present inventionwill be explained in further detail with reference to the attacheddrawings, in which:

[0024]FIG. 1 is a sectional view of a multi-layer ceramic capacitoraccording to an embodiment of the present invention;

[0025]FIG. 2 is TEM photograph of a dielectric ceramic compositionaccording to an example of the present invention;

[0026]FIG. 3 is a graph of the distribution of MnO in the ferroelectricphase region in the photograph shown in FIG. 2;

[0027]FIG. 4A and FIG. 4B are graphs of the temperature characteristicof Example 1 and Comparative Example 4 in the examples of the presentinvention; and

[0028]FIG. 5A and FIG. 5B are graphs of the voltage characteristics ofExamples 1 and 18 in the examples of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Multi-layer Ceramic Capacitor

[0029] As shown in FIG. 1, a multi-layer ceramic capacitor 1 accordingto an embodiment of the present invention has a capacitor device body 10of a configuration of dielectric layers 2 and internal electrode layers3 stacked alternately. At the two ends of the capacitor device body 10are formed a pair of external electrodes 4 conductive with the internalelectrode layers 3 alternately arranged inside the device body 10. Theshape of the capacitor device body 10 is not particularly limited, butnormally is made a parallelopiped. Further, the dimensions are notparticularly limited and may be made suitable dimensions in accordancewith the application. Usually, however, they are (0.6 to 5.6 mm)×(0.3 to5.0 mm)×(0.3 to 1.9 mm).

[0030] The internal electrode layers 3 are stacked so that end facesthereof alternately protrude out to the surfaces of the two opposingends of the capacitor device body 10. The pair of external electrodes 4are formed at the two ends of the capacitor device body 10 and areconnected to the exposed end faces of the alternately arranged internalelectrode layers 3, thereby constructing a capacitor circuit.

Dielectric Layers 2

[0031] Each of the dielectric layers 2 contains the dielectric ceramiccomposition of the present invention.

[0032] The dielectric ceramic composition of the present invention is adielectric ceramic composition comprising as main components bariumtitanate (BaTiO₃) and a component M (wherein M is at least one type ofcomponent selected from manganese oxide (MnO), iron oxide (FeO), cobaltoxide (CoO), and nickel oxide (NiO)) and having a ferroelectric phaseregion, wherein the concentration of the component M in theferroelectric phase region changes from the outside toward the centerthereof.

[0033] For example, as shown in FIG. 2 and FIG. 3, the dielectricceramic composition according to the present invention has a crystalgrain comprised of a diffusion phase region and a ferroelectric phaseregion. The ferroelectric phase region is comprised of an outsideferroelectric phase region and an inside ferroelectric phase region. Thedielectric ceramic composition of the embodiment shown in FIG. 2 andFIG. 3 is a dielectric ceramic composition comprised of barium titanate(BaTiO₃) and manganese oxide (MnO) as main components.

[0034] The grain boundary of the crystal grains are judged from the TEMphotograph shown in FIG. 2 for example. Further, the phase boundarybetween the diffusion phase region and ferroelectric phase region issimilarly judged from the TEM photograph. The phase boundary between theoutside ferroelectric phase region and the inside ferroelectric phaseregion in the ferroelectric phase region cannot be judged from the TEMphotograph shown in FIG. 2.

[0035] As shown in FIG. 2, six analysis points I to VI are taken fromthe grain boundary to center of a crystal grain and the concentration ofMnO at each analysis point were measured. The results are shown in FIG.3. As shown in FIG. 3, the ferroelectric phase region of the presentembodiment changes in concentration of MnO from the outside to thecenter and further has a concentration of MnO increasing close to thephase boundary between the diffusion phase and ferroelectric phaseregion compared with close to the center of the region. Further, theferroelectric phase region has an outside region which contains MnO andhas this distribution of concentration and an inside region which doesnot include much MnO at all. The outside region will be referred to the“outside ferroelectric phase region” and the inside region will bereferred to as the “inside ferroelectric phase region”. The phaseboundary between the outside ferroelectric phase region and insideferroelectric phase region cannot be judged from the TEM photographshown in FIG. 2.

[0036] In the composition of the present invention, the molar ratio(M/A+B) of the component M to the total barium titanate (A+B) in thecomposition is not particularly limited, but is preferably 0.0005 to0.01, more preferably 0.001 to 0.007.

[0037] Further, the subcomponents which can be included in thecomposition according to the present invention are not particularlylimited, but at least one type of oxide selected from MgO, CaO, BaO,SrO, and Cr₂O₃ and/or compounds forming oxides upon firing (for example,MgCO₃) may be mentioned.

[0038] As other additives, SiO₂, Al₂O₃, and other sintering aids may bementioned. These types of sintering aids have actions of reducing thesintering temperature. Further, they do not have much of an effect onthe capacity-temperature characteristic.

[0039] Further, as other subcomponents, at least one type of oxideselected from V₂O₅, MoO₃, and WO₃ may be mentioned.

[0040] As still other subcomponents, Y and other rare earth elementoxides may be illustrated.

[0041] The multi-layer ceramic capacitor using the dielectric ceramiccomposition of the present invention is suitable for use as anelectronic device for equipment used at an environment of 80° C. ormore, particularly 85 to 125° C. Further, in this temperature range, thecapacity-temperature characteristic simultaneously satisfies the Bcharacteristic of the EIAJ standard [rate of change of capacity ofwithin ±10% at −25 to 85° C. (reference temperature 20° C.)] and the X7Rcharacteristic of the EIA standard (−55 to 125° C., ΔC/C=±15% or less).

[0042] In a multi-layer ceramic capacitor, the dielectric layers arenormally subjected to an AC electric field and a DC electric fieldsuperposed over this, but the temperature characteristic of the capacityis extremely stable even when such electric fields are applied.

Internal Electrode Layers 3

[0043] The electroconductive material contained in the internalelectrode layers 3 is not particularly limited, but a base metal may beused since the material constituting the dielectric layers 2 hasresistance to reduction. As the base metal used as the electroconductivematerial, Ni or a Ni alloy is preferable. As the Ni alloy, an alloy ofat least one type of element selected from Mn, Cr, Co, and Al with Ni ispreferable. The content of the Ni in the alloy is preferably not lessthan 95 wt %.

[0044] Note that the Ni or Ni alloy may contain P and other varioustypes of trace components in amounts of not more than 0.1 wt % or so.

[0045] The thickness of the internal electrode layers may be suitablydetermined in accordance with the application etc., but is usually 0.5to 5 μm, preferably 0.5 to 2.5 μm.

External Electrodes 4

[0046] The electroconductive material contained in the externalelectrodes 4 is not particularly limited, but in the present inventionan inexpensive Ni, Cu, or alloys of the same may be used.

[0047] The thickness of the external electrodes may be suitablydetermined in accordance with the application etc., but is usually 10 to100 μm or so.

Method of Manufacturing Multi-Layer Ceramic Capacitor

[0048] The multi-layer ceramic capacitor produced using the dielectricceramic composition of the present invention is produced by preparing agreen chip using the usual printing method or sheet method which usespastes, firing the green chip, then printing or transferring andsintering the external electrodes. The method of manufacture will beexplained in detail below.

[0049] The dielectric layer paste may be an organic-based coatingobtained by mixing the dielectric layer ingredient and an organicvehicle and may be a water-based coating.

[0050] For the dielectric ingredient, the above oxides or their mixturesor composite oxides may be used, but it is also possible to suitablyselect and mix for use various compounds forming the above oxides orcomposite oxides after firing, for example, carbonates, oxalates,nitrates, hydroxides, and organic metal compounds. The content of thesecompounds in the dielectric ingredient may be determined so as to givethe above composition of the dielectric ceramic composition afterfiring.

[0051] The dielectric ingredient is usually used in the form of a powderof an average grain size of 0.1 to 1 μm.

[0052] Note that when preparing the dielectric ingredient, the bariumtitanate (A) and component M are calcined, then the compound obtained atthe calcination step and further barium titanate (B) are mixed toprepare the dielectric ingredient. The calcination temperature is notparticularly limited, but is preferably 1000 to 1300° C., morepreferably 1000 to 1100° C. If the calcination temperature is too low,DC bias voltage characteristic tends to become worse. If the temperatureis too high, pulverization after calcination becomes difficult andpreparation of the dielectric ingredient tends to become hard.

[0053] The molar ratio (M/A) of the component M to the barium titanate(A) is not particularly limited, but is preferably 0.0010 to 0.0120,more preferably 0.0020 to 0.0080. Furter, the molar ratio (B/A) of thelater added barium titanate (B) to the pre-calcination barium titanate(A) is not particularly limited, but is preferably 0.05 to 5.00, morepreferably 0.10 to 1.00. By using these molar ratios, it is possible toeasily obtain a dielectric ceramic composition having a ferroelectricphase region where the concentration of the component M changes from theoutside to the center and superior characteristics can be exhibited.Note that when the ratio M/A is too large, the dielectric constant tendsto fall.

[0054] The organic vehicle used in the paste is comprised of a binderdissolved in an organic solvent. The binder used for the organic vehicleis not particularly limited, but may be suitably selected from ethylcellulose, polyvinyl butyral, and other ordinary types of binders.Further, the organic solvent used is also not particularly limited andmay be suitably selected from terpineol, butyl carbitol, acetone,toluene, and other organic solvents in accordance with the printingmethod, sheet method, or other method of use.

[0055] Further, when using a water-based coating as the dielectric layerpaste, it is sufficient to knead a water-based vehicle comprised of awater-based binder or dispersant etc. dissolved in water together withthe dielectric layer ingredient. The water-based binder used for thewater-based vehicle is not particularly limited. For example, apolyvinyl alcohol, cellulose, water-based acrylic resin, etc. may beused.

[0056] The internal electrode layer paste is prepared by kneading theelectroconductive material comprised of the above various types ofelectroconductive metals and alloys or various types of oxides formingthe above electroconductive materials after firing, an organic metalcompound, resinate, etc. together with the above organic vehicle.

[0057] The external electrode paste may be prepared in the same way asthe above internal electrode layer paste.

[0058] The content of the organic vehicle in the above pastes is notparticularly limited and may be within the usual content, for example,the binder may be contained in an amount of 1 to 5 wt % or so and thesolvent 10 to 50 wt % or so. Further, the pastes may include, inaccordance with need, various types of additives selected fromdispersants, plasticizers, dielectrics, insulators, etc. The totalcontent of these is preferably not more than 10 wt %.

[0059] When using a printing method, the dielectric layer paste and theinternal electrode layer paste are successively printed on the PET orother substrate. The result is then cut into a predetermined shape, thenthe pastes are peeled off from the substrate to form a green chip.

[0060] Further, when using a sheet method, a dielectric layer paste isused to form a green sheet, the internal electrode layer paste isprinted on top of this, then these are stacked to form a green chip.

[0061] Before firing, the green chip is processed to remove the binder.This processing for removing the binder may be performed under ordinaryconditions. If Ni or a Ni alloy or another base metal is used for theelectroconductive material of the internal electrode layers, theprocessing is preferably performed under the following conditions:

[0062] Rate of temperature rise: 5 to 300° C./hour, in particular 10 to100° C./hour

[0063] Holding temperature: 180 to 400° C., in particular 200 to 300° C.

[0064] Temperature holding time: 0.5 to 24 hours, in particular 5 to 20hours

[0065] Atmosphere: in the air

[0066] The atmosphere when firing the green chip may be suitablydetermined in accordance with the type of the electroconductive materialin the internal electrode layer paste, but when using Ni or a Ni alloyor another base metal as the electroconductive material, the oxygenpartial pressure in the sintering atmosphere is preferably made 10⁻⁸ to10⁻¹⁵ atmospheres. If the oxygen partial pressure is less than thisrange, the electroconductive material of the internal electrode layersbecomes abnormally sintered and ends up breaking in the middle in somecases. Further, if the oxygen partial pressure is more than the aboverange, the internal electrode layers tend to oxidize.

[0067] Further, the holding temperature at the time of firing ispreferably 1100 to 1400° C., more preferably 1200 to 1360° C., stillmore preferably 1200 to 1320° C. If the holding temperature is less thanthe above range, the densification becomes insufficient, while if overthat range, there is a tendency toward breaking of the electrodes due toabnormal sintering of the internal electrode layers, deterioration ofthe capacity-temperature characteristic due to dispersion of thematerial comprising the internal electrode layers, and reduction of thedielectric ceramic composition.

[0068] The various conditions other than the above conditions arepreferably selected from the following ranges:

[0069] Rate of temperature rise: 50 to 500° C./hour, in particular 200to 350° C./hour

[0070] Temperature holding time: 0.5 to 8 hours, in particular 1 to 3hours

[0071] Cooling rate: 50 to 500° C./hour, in particular 200 to 350°C./hour

[0072] Note that the sintering atmosphere is preferably a reducingatmosphere. As the atmospheric gas, for example, it is preferable to usea wet mixed gas of N₂ and H₂.

[0073] When firing in a reducing atmosphere, the capacitor device bodyis preferably annealed. The annealing process is for reoxidizing thedielectric layers. Since this enables the insulation resistance lifetimeto be remarkably prolonged, the reliability is improved.

[0074] The oxygen partial pressure in the annealing atmosphere ispreferably at least 10⁻⁹ atmospheres, particularly 10⁻⁶ to 10⁻⁹atmospheres. If the oxygen partial pressure is less than the aboverange, reoxidation of the dielectric layers is difficult, while if overthat range, the internal electrode layers tend to oxide.

[0075] The holding temperature at the time of annealing is preferablynot more than 1100° C., in particular 500 to 1100° C. If the holdingtemperature is less than the above range, the oxidation of thedielectric layers becomes insufficient, so that the insulationresistance tends to become low and the insulation resistance lifetimeshort. On the other hand, when the holding temperature exceeds the aboverange, not only do the internal electrode layers oxidize and thecapacity fall, but also the internal electrode layers end up reactingwith the dielectric material resulting in a tendency towarddeterioration of the capacity-temperature characteristic, a fall in theinsulation resistance, and a fall in the insulation resistance lifetime.Note that the annealing may be comprised of only a temperature raisingprocess and temperature reducing process. That is, the temperatureholding time may also be made zero. In this case, the holdingtemperature is synonymous with the maximum temperature.

[0076] The various conditions other than the above conditions arepreferably determined from the following ranges:

[0077] Temperature holding time: 0 to 20 hours, in particular 6 to 10hours

[0078] Cooling rate: 50 to 500° C./hour, in particular 100 to 300°C./hour

[0079] Note that for the atmospheric gas, wet N₂ gas etc. may be used.

[0080] In the steps of removing the binder, the firing, and theannealing, for example, a wetter etc. may be used to wet the N₂ gas ormixed gas. In this case, the temperature of the water is preferably 5 to75° C.

[0081] The steps of removing the binder, firing, and annealing may beperformed consecutively or independently. When preferably performingthese consecutively, after processing to remove the binder, theatmosphere is changed without cooling, then the temperature is raised tothe holding temperature for firing, the firing performed, then the chipis cooled, the atmosphere is changed when the holding temperature of theannealing is reached, and then annealing is performed. On the otherhand, when performing these independently, at the time of firing,preferably the temperature is raised to the holding temperature at thetime of the processing for removing the binder in an N₂ gas or wet N₂gas atmosphere, then the atmosphere is changed and the temperature isfurther raised. Preferably, the chip is cooled to the holdingtemperature of the annealing, then the atmosphere changed again to an N₂gas or wet N₂ gas atmosphere and the cooling continued. Further, at thetime of annealing, the temperature may be raised to the holdingtemperature in an N₂ gas atmosphere, then the atmosphere changed or theentire annealing process may be performed in a wet N₂ gas atmosphere.

[0082] The thus obtained capacitor device body is, for example, endpolished using barrel polishing or sandblasting etc., then printed ortransferred with an external electrode paste and fired to form theexternal electrodes 4. The firing conditions of the external electrodepaste are for example preferably 400 to 800° C. for 10 minutes to 1 houror so in a wet mixed gas of N₂ and H₂. Further, in accordance with need,the surfaces of the external electrodes 4 may be provided with acovering layer using a plating technique etc.

[0083] The thus produced multi-layer ceramic capacitor of the presentinvention is mounted by soldering it onto a printed circuit board foruse in various types of electronic equipment.

[0084] Note that the present invention is not limited to the aboveembodiment and may be modified in various ways within the scope of theinvention.

[0085] For example, in the above embodiment, the multi-layer ceramiccapacitor was explained as an example of the electronic device accordingto the present invention, but the electronic device according to thepresent invention is not limited to the multi-layer ceramic capacitor.It may be any device having dielectric layers comprised of thedielectric ceramic composition of the above composition.

[0086] Below, the present invention will be explained with reference tomore detailed examples, but the present invention is not limited tothese examples.

EXAMPLE 1

[0087] First, 0.5 mol % of MnCO₃ was weighed for 100 mol % of bariumtitanate (A) comprised of BaTiO₃. These were mixed with pure water in azirconia ball by means of a ball mill for 16 hours. Next, the mixturewas dried by evaporating the moisture in a high temperature tank of 130°C. The powder obtained after the drying was calcined at 1100° C. toobtain a mixture of BaTiO₃ and MnO. Note that the calcination may beperformed in a reducing atmosphere or even in the air.

[0088] 50 mol % of later adding barium titanate (B), 2.5 mol % of MgCO₃,2.5 mol % of Y₂O₃, 1.5 mol % of CaCO₃, and 4 mol % of SiO₂ were weighedwith respect to 100 mol % of the pre-calcination barium titanate (A).These were mixed together with the calcined BaTiO₃ and MnO mixture withpure water in a zirconia ball by means of a ball mill for 16 hours.Next, this mixture was dried by evaporating the moisture in a hightemperature tank of 130° C. to obtain the dielectric ingredient.

[0089] Note that the pre-calcination barium titanate (A) and lateradding barium titanate (B) may be the same in grain size or different ingrain size. The methods of manufacture may be the same or different. Forexample, these barium titanates may be obtained by the solid phasemethod, oxalate method, hydrothermal synthesis method, alkoxide method,or sol gel method. Further, the grain sizes are not particularlylimited, but for example may be 0.1 to 1.0 μm.

[0090] Next, 100 wt % of the above dielectric ingredient, 4.8 wt % ofacrylic resin, 40 wt % of methylene chloride, 20 wt % of ethyl acetate,6 wt % of mineral spirit, and 4 wt % of acetone were mixed in a ballmill to form a paste and obtain the dielectric layer paste.

[0091] For the internal electrode layer paste, 44.6 wt % of nickelparticles of an average grain size of 0.4 μm, 52.0 wt % of terpineol, 3wt % of ethyl cellulose, and 0.4 wt % of benzotriazole were kneadedusing a triple-roll to make a paste.

[0092] For the external electrode paste, 100 wt % of copper particles ofan average grain size of 0.5 μm, 35 wt % of an organic vehicle (8 wt %of ethyl cellulose dissolved in 92 wt % of butyl carbitol), and 7 wt %of butyl carbitol were kneaded together by a triple-roll to make apaste.

[0093] The above dielectric layer paste was used to form a green sheetof a thickness of 30 μm on a PET film. The internal electrode paste wasprinted on this, then the green sheet was peeled from the PET film. Thethus obtained green sheet was stacked and pressed to obtain a greenchip. Four green sheets having the internal electrodes were stacked.

[0094] The green chip was cut to predetermined sizes which were thenprocessed to remove the binder, fired, and annealed to obtainmulti-layer ceramic sintered bodies. The size of the sintered sampleswas 3.2 mm×1.6 mm×0.6 mm. The thickness of the dielectric layer wasabout 20 μm, while the thickness of the internal electrode layer was 2μm.

[0095] Next, the end faces of the multi-layer ceramic sintered bodieswere polished by sandblasting, then the external electrode paste wastransferred to the end faces and the bodies were fired in a wet nitrogengas and hydrogen gas atmosphere at 800° C. for 10 minutes to form theexternal electrodes and obtain the multi-layer ceramic capacitorsamples.

[0096] The processing to remove the binder was performed under thefollowing conditions:

[0097] Rate of temperature rise: 15° C./hour

[0098] Holding temperature: 240° C.

[0099] Temperature holding time: 8 hours

[0100] Atmosphere: in the air

[0101] The firing was performed under the following conditions:

[0102] Rate of temperature rise: 300° C./hour

[0103] Holding temperature: 1275° C.

[0104] Temperature holding time: 2 hours

[0105] Cooling rate: 300° C./hour

[0106] Atmospheric gas: wet N₂+H₂ mixed gas

[0107] Oxygen partial pressure: 10⁻¹² atmospheres

[0108] The annealing was performed under the following conditions:

[0109] Holding temperature: 1050° C.

[0110] Temperature holding time: 2 hours

[0111] Cooling rate: 300° C./hour

[0112] Atmospheric gas: wet N₂ gas

[0113] Oxygen partial pressure: 10⁻⁶ atmospheres

[0114] The multi-layer ceramic capacitor samples obtained in this waywere measured for relative dielectric constant (ε), dielectric loss(tanδ), and capacity-temperature characteristic. The multi-layer ceramiccapacitors were measured for electrostatic capacity and dielectric loss(tanδ) under conditions of 1 kHz and 1 Vrms using an LCR meter. Therelative dielectric constant (ε) was calculated from the obtainedelectrostatic capacity, electrode dimensions, and distance betweenelectrodes. The results are shown in Table 1. TABLE 1 Comp. BaTiO, Calc.Volt. Sample M/BaTiO₃ (B)/BaT temp. Temp. char. tanδ IR (Ω) Judg- no.Comp. M (A) iO₃ (A) (° C.) ε char. (%) (%) 100V ment Reasons Ex. 1 MnO0.0050 0.5 1100 2300 G −5 0.46 6.9E+11 VG Ex. 2 FeO 0.0050 0.5 1100 2100G −10 0.60 7.5E+11 VG Ex. 3 CoO 0.0050 0.5 1100 2200 G −5 0.48 7.2E+11VG Ex. 4 NiO 0.0050 0.5 1100 2400 G −15 0.58 6.6E+11 VG Ex. 5 MnO 0.00100.5 1100 3500 G −32 0.75 4.5E+11 G Volt. char. Ex. 6 MnO 0.0020 0.5 11002900 G −25 0.60 5.5E+11 VG Ex. 7 MnO 0.0120 0.5 1100 1800 G −20 0.438.8E+11 VG Ex. 8 MnO 0.0500 0.5 1100 1500 G +5 0.41 7.0E+11 G ε low C.Ex. MnO 0.0013 0 1100 1200 P −10 0.40 1.3E+12 P Temp. char., ε 1 low C.Ex. MnO 0.0033 0 1100 1100 P −5 0.35 1.4E+12 P Temp. char., ε 2 low C.Ex. MnO 0.0080 0 1100 900 P −3 0.30 1.8E+12 P Temp. char., ε 3 low C.Ex. MnO 0.0050 0 1100 1000 P −4 0.33 1.6E+12 P Temp. char., ε 4 low C.Ex. MnO 0.0050 0.01 1100 1000 P −4 0.33 1.6E+12 P Temp. char., ε 5 lowEx. 9 MnO 0.0050 0.05 1100 1600 G −5 0.40 9.9E+11 VG Ex. 10 MnO 0.00500.1 1100 1700 G −6 0.43 9.3E+11 VG Ex. 11 MnO 0.0050 0.3 1100 1900 G −70.47 8.3E+11 VG Ex. 12 MnO 0.0050 0.8 1100 2500 G −7 0.50 6.3E+11 VG Ex.13 MnO 0.0050 1 1100 2500 G −10 0.52 6.3E+11 VG Ex. 14 MnO 0.0050 2 11002600 G −15 0.55 6.1E+11 VG Ex. 15 MnO 0.0050 3 1100 2800 G −19 0.585.6E+11 VG Ex. 16 MnO 0.0050 4 1100 3000 G −27 0.63 5.3E+11 VG Ex. 17MnO 0.0050 5 1100 3100 G −40 0.70 5.1E+11 G Volt. char. Ex. 18 MnO0.0050 0.5 900 2400 G −30 0.75 6.6E+11 G Volt. char. Ex. 19 MnO 0.00500.5 1000 2400 G −10 0.63 6.6E+11 VG Ex. 20 MnO 0.0050 0.5 1050 2300 G +50.42 6.9E+11 VG Ex. 21 MnO 0.0050 0.5 1100 2300 G +5 0.46 6.9E+11 VG Ex.22 MnO 0.0050 0.5 1200 2300 G +5 0.45 6.9E+11 VG Ex. 23 MnO 0.0050 0.51300 2300 G +5 0.49 6.9E+11 VG Ex. 24 MnO 0.0050 0.5 1400 2400 G +5 0.496.6E+11 G Pulv. diff. after calcin.

[0115] For the temperature characteristic of the capacity, themulti-layer ceramic capacitor samples were measured for electrostaticcapacity at a voltage of 1V for a temperature −range of −55° C. to 125°C. using the LCR meter. A rate of change of capacity using a referencetemperature of 25° C. of within ±15% in the range of −55° C. to 125° C.(X7R of EIA standard) was deemed as an X7R temperature characteristic.Samples satisfying this were evaluated as “good (G)”, while those notsatisfying it were evaluated as “poor (P)”. The results are shown inFIG. 4A and Table 1. As shown in FIG. 4A and Table 1, Example 1 wasconfirmed to satisfy the X7R characteristic.

[0116] Further, the capacitor samples were measured for insulationresistance (IR) at 25° C. The voltage when measuring the insulationresistance (IR) was DC 100V. The value 60 seconds after the start ofapplication was used (unit of Ω). The results are shown in Table 1.

[0117] Further, the capacitor samples were measured for voltagecharacteristic. Table 1 shows as the voltage characteristic the rate ofchange of capacity (ΔC/C, %) when applying a DC bias voltage of 2V/μm tothe capacitor samples. Further, the rate of change of capacity (ΔC/C, %)with respect to the DC bias voltage in the sample of Example 1 wasgraphed in FIG. 5A. Example 1 was confirmed to have a small rate ofchange of capacity even under a high DC voltage.

[0118] Further, the dielectric layer of a capacitor sample wasphotographed using a transmission electron microscope (TEM, made byNippon Denshi, JEM-2000FXII). The results are shown in FIG. 2. In FIG.2, six analysis points I to VI were taken from the grain boundary to thecenter of a crystal grain and the concentration of MnO were measuredusing EDS (TN5402 made by Noran Instruments). The results are shown inFIG. 3. As shown in FIG. 3, the ferroelectric phase region of Example 1exhibits a change in concentration of MnO from the outside to thecenter. Further, the concentration of MnO was confirmed to rise at theoutside compared with near the center of the region. Further, theferroelectric phase region was confirmed to consist of an outside regionwith a distribution of concentration of MnO and an inside region notcontaining much MnO at all.

[0119] Note that in the results of judgment of Table 1, samplessatisfying the X7R characteristic and superior in the othercharacteristics as well (ε, voltage characteristic, tanδ, IR) areindicated as “very good (VG)”, samples satisfying the X7R characteristicbut inferior in one of the other characteristic as “good (G)”, andsamples not satisfying the X7R characteristic as “poor (P)”.

EXAMPLES 2 TO 4

[0120] The same procedure was followed as in Example 1 except, as shownin Table 1, for using FeO, CoO, or NiO instead of MnO, to preparecapacitor samples. These were tested in the same way as in Example 1. Asshown in Table 1, the samples were confirmed to have similar superiorcharacteristics as in Example 1 in the dielectric constant (ε),temperature characteristic, voltage characteristic, dielectric loss(tanδ), and insulation resistance (IR).

EXAMPLES 5 TO 8

[0121] The same procedure was followed as in Example 1 except, as shownin Table 1, for changing the molar ratio (M/A) of MnO to thepre-calcination barium titanate (A) to 0.1 mol %, 0.2 mol %, 1.2 mol %,and 5 mol %, to prepare capacitor samples. These were tested in the sameway as in Example 1. As shown in Table 1, the samples were confirmed tohave similar superior characteristics as in Example 1 in the dielectricconstant (ε), temperature characteristic, voltage characteristic,dielectric loss (tanδ), and insulation resistance (IR). Example 5,however, was confirmed to have an inferior voltage characteristic to theother examples since the ratio of MnO was too small. Further, Example 8was confirmed to have a low dielectric constant due to the overly largeM/A.

Comparative Examples 1 to 5

[0122] The same procedure was followed as in Example 1 except, as shownin Table 1, for changing the molar ratio (M/A) of MnO to thepre-calcination barium titanate (A) and preparing the dielectricingredients without additionally adding later adding barium titanate (B)after the calcination, to prepare capacitor samples. For justComparative Example 5, unlike Comparative Examples 1 to 4, later addingbarium titanate (B) was additionally added, but the molar ratio (B/A) ofthe amount added was a small 1 percent. These were tested in the sameway as in Example 1.

[0123] As shown in Table 1, Comparative Examples 1 to 5 were confirmedto have low dielectric constants (ε) compared with the examples of theinvention and not to satisfy the X7R characteristic (deterioration oftemperature characteristic). Note that a graph of the temperaturecharacteristic of the sample of Comparative Example 4 is shown in FIG.4B.

[0124] Further, in the same way as in Example 1, six analysis points Ito VI were taken from the grain boundary to the center of the crystalgrain of each of the dielectric layers of the capacitor samples ofComparative Examples 1 to 5 and the concentrations of MnO measured. As aresult, almost no change in concentration of MnO was observed from theoutside to the center and the concentrations were confirmed to besubstantially uniform.

EXAMPLES 9 TO 17

[0125] The same procedure was followed as in Example 1 except, as shownin Table 1, for changing the molar ratio (B/A) of later adding bariumtitanate (B) to the pre-calcination barium titanate (A), to preparecapacitor samples. These were tested in the same way as in Example 1.

[0126] As shown in Table 1, the samples were confirmed to have similarsuperior characteristics as in Example 1 in the dielectric constant (ε),temperature characteristic, voltage characteristic, dielectric loss(tanδ), and insulation resistance (IR). Example 17, however, wasconfirmed to have an inferior voltage characteristic to the otherexamples since the molar ratio B/A was too large.

EXAMPLES 18 TO 24

[0127] The same procedure was followed as in Example 1 except, as shownin Table 1, for changing the calcination temperature, to preparecapacitor samples. These were tested in the same way as in Example 1.

[0128] As shown in Table 1, the samples were confirmed to have similarsuperior characteristics as in Example 1 in the dielectric constant (ε),temperature characteristic, voltage characteristic, dielectric loss(tanδ), and insulation resistance (IR). Example 18, however, wasconfirmed to have an inferior voltage characteristic to the otherexamples since the calcination temperature was too low. The voltagecharacteristic of the sample in Example 18 is shown in FIG. 5B. Further,Example 24 was hard to pulverize after calcination.

[0129] As explained above, according to the present invention, it ispossible to provide an electronic device such as a multi-layer capacitorwhich can satisfy both of the X7R characteristic (EIA standard) and Bcharacteristic (EIAJ standard) of the temperature characteristic of theelectrostatic capacity, has little voltage dependency of theelectrostatic capacity and the insulation resistance, is superior ininsulation breakdown resistance, and can use Ni or a Ni alloy as theinternal electrode layer, a dielectric ceramic composition suitable foruse as the dielectric layer of such an electronic device, and a methodof producing the same.

1. A dielectric ceramic composition comprising as main components bariumtitanate and a component M (wherein M is at least one type of componentselected from manganese oxide, iron oxide, cobalt oxide, and nickeloxide) and having a ferroelectric phase region, wherein theconcentration of the component M in the ferroelectric phase regionchanges from the outside toward the center thereof.
 2. The dielectricceramic composition as set forth in claim 1 , wherein the concentrationof the component M in the ferroelectric phase region is higher at theoutside compared with near the center of the ferroelectric phase region.3. The dielectric ceramic composition as set forth in claim 1 , whereinthe ferroelectric phase region is comprised of an outside ferroelectricphase region and an inside ferroelectric phase region and has a higherconcentration of the component M in the outside ferroelectric phaseregion than the inside ferroelectric phase region.
 4. The dielectricceramic composition as set forth in claim 3 , wherein the insideferroelectric phase region does not contain almost any of the componentM.
 5. The dielectric ceramic composition as set forth in any one ofclaims 1 to 4 , wherein there is a diffusion phase region outside of theferroelectric phase region.
 6. A method of producing a dielectricceramic composition comprising the steps of; calcining barium titanate(A) and an ingredient of a component M (where M is at least one type ofcomponent selected from a manganese oxide, iron oxide, cobalt oxide, andnickel oxide), and firing a mixture of the compound obtained in thecalcination step and other barium titanate (B).
 7. The method ofproducing a dielectric ceramic composition as set forth in claim 6 ,wherein the temperature at the calcination is 1000 to 1300° C.
 8. Themethod of producing a dielectric ceramic composition as set forth inclaim 6 or 7 , wherein the firing is performed under a reducingatmosphere.
 9. The method of producing a dielectric ceramic compositionas set forth in claim 6 , wherein the molar ratio (M/A) of the componentM to the pre-calcination barium titanate (A) is 0.0010 to 0.0120. 10.The method of producing a dielectric ceramic composition as set forth inclaim 7 , wherein the molar ratio (M/A) of the component M to thepre-calcination barium titanate (A) is 0.0010 to 0.0120.
 11. The methodof producing a dielectric ceramic composition as set forth in claim 8 ,wherein the molar ratio (M/A) of the component M to the pre-calcinationbarium titanate (A) is 0.0010 to 0.0120.
 12. The method of producing adielectric ceramic composition as set forth in claim 9 , wherein themolar ratio (B/A) of the later adding barium titanate (B) to thepre-calcination barium titanate (A) is 0.05 to 5.00.
 13. The method ofproducing a dielectric ceramic composition as set forth in claim 10 ,wherein the molar ratio (B/A) of the later adding barium titanate (B) tothe pre-calcination barium titanate (A) is 0.05 to 5.00.
 14. The methodof producing a dielectric ceramic composition as set forth in claim 11 ,wherein the molar ratio (B/A) of the later adding barium titanate (B) tothe pre-calcination barium titanate (A) is 0.05 to 5.00.
 15. Anelectronic device having a dielectric layer, wherein the dielectriclayer comprises of a dielectric ceramic composition comprising as maincomponents barium titanate and a component M (wherein M is at least onetype of component selected from manganese oxide, iron oxide, cobaltoxide, and nickel oxide) and having a ferroelectric phase region and theconcentration of the component M in the ferroelectric phase regionchanges from the outside toward the center thereof.
 16. The electronicdevice as set forth in claim 15 , further comprising an internalelectrode layer including nickel or a nickel alloy.